The present invention relates to method and apparatus for holding a billet while closing a pressure chamber during hydrostatic extrusion. The method can be used in a press where, upon inserting the billet, the pressure chamber during closing is supplied with a pressure medium at the end where a pressure-generating piston is inserted to generate the necessary extrusion pressure. The supplied pressure medium achieves a holding force which holds the billet and a die pressed against a die support, thus fixing the billet and the die in a definite, desired position during the closing of the pressure chamber.
In a known press of the kind mentioned, there is a billet-holding piston with valve members which, when there is a certain pressure difference between the two sides of the piston, allows pressure medium to pass from a space on one side of the piston to a space on its other side. When the movement of the piston is prevented by contact with an inserted billet, the pressure increases in the space on one side of the piston until the valve member is opened so that pressure medium passes the piston. The difference in pressure results in a force which may be utilized to hold a billet and a die during the closing of the pressure chamber. Such a press is described in detail in U.S. Pat. No. 3,531,965.